Mechanical and chemical-mechanical planarization processes (“CMP”) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly. FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate 12. The planarizing machine 10 has a support table 14 with a top-panel 16 at a workstation where an operative portion (A) of a planarizing pad 40 is positioned. The top-panel 16 is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad 40 may be secured during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the planarizing pad 40 over the top-panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide or pre-operative portion of the planarizing pad 40, and the take-up roller 23 carries a used or post-operative portion of the planarizing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the planarizing pad 40 over the top-panel 16 to hold the planarizing pad 40 stationary during operation. A motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the planarizing pad 40 across the top-panel 16. Accordingly, clean pre-operative sections of the planarizing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. Several nozzles 33 attached to the substrate holder 32 dispense a planarizing solution 44 onto a planarizing surface 42 of the planarizing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the substrate holder 32 via a terminal shaft 39 such that the drive assembly 35 orbits the substrate holder 32 about an axis B—B (as indicated by arrow R1). The terminal shaft 39 may also rotate the substrate holder 32 about its central axis C—C (as indicated by arrow R2).
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 used in the web-format planarizing machine 10 is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is a “clean solution” without abrasive particles because the abrasive particles are fixedly distributed across the planarizing surface 42 of the planarizing pad 40. In other applications, the planarizing pad 40 may be a non-abrasive pad without abrasive particles, composed of a polymeric material (e.g., polyurethane) or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals to remove material from a substrate.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44. The drive assembly 35 then orbits the substrate holder 32 about the axis B—B and optionally rotates the substrate holder 32 about the axis C—C to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
The CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrate assemblies develop large “step heights” that create a highly topographic surface across the substrate assembly. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several intermediate stages during substrate assembly processing because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on non-uniform substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
One problem with conventional CMP methods is that the planarizing surface 42 of the planarizing pad 40 can become glazed with accumulations of slurry and/or material removed from the substrate 12 or the planarizing pad 40. One conventional approach to addressing this problem is to remove the accumulations by conditioning the planarizing pad 40, for example, by abrading the planarizing pad 40 with an abrasive disk (not shown). A drawback with this approach is that the equipment required for conditioning the planarizing pad 40 adds complexity to the planarizing machine 10 and, if the conditioning operation is performed separately from the planarizing operation, it reduces the time that the planarizing pad 40 is available for planarizing. Conventional conditioning processes can thus limit the overall efficiency of the apparatus.
One approach to address this drawback is to eliminate the need to condition the pad by making the planarizing surface or the entire planarizing pad disposable. For example, U.S. application Ser. No. 09/001,333 discloses a disposable planarizing pad film made from materials such as Mylar or polycarbonate. The pads disclosed in application Ser. No. 09/011,333 can have microfeatures of different heights that entrap small volumes of an abrasive slurry and maintain the slurry in contact with the substrate. The microfeatures can be formed using a variety of techniques, such as embossing or photo-patterning.
One conventional method for photo-patterning is shown schematically in FIGS. 2A–2E. As shown in FIG. 2A, a photopolymer composite 50 is formed by disposing a photopolymer resist material 53 on a substrate polymer 52 which is supported by support layer 51. The photopolymer resist material 53 is then exposed to a radiation source 63. A mask 60 having opaque portions 61 and transmissive portions 62 blocks the radiation emitted from the radiation source 63 from striking unexposed portions 55 of the photopolymer resist material 53, while allowing the radiation to strike exposed portions 54.
As shown schematically in FIG. 2B, the exposed portions 54 change chemical characteristics as a result of being exposed to the radiation source 63. For example, when the photopolymer resist material 53 is initially soluble in a selected solvent, exposure to the selected radiation can change the exposed portions 54 to become insoluble in the selected solvent. Alternatively, when the photopolymer resist material is initially insoluble in the selected solvent, exposure to the selected radiation can make the exposed portions 54 soluble. In either case, the solubility of the unexposed portions 55 remains unchanged.
When the exposed portions 54 are rendered insoluble by exposure to the selected radiation, FIG. 2C schematically illustrates the photopolymer composite 50 after being rinsed with the selected solvent. The exposed portions 54 of the photopolymer resist material 53 remain intact and the unexposed portions have been removed by the solvent to expose the substrate polymer 52 below. The substrate polymer 52 is then etched to remove the portions of the substrate polymer material from between the exposed portions 54 of the photopolymer resist material 53 and form recesses 70, as is shown in FIG. 2D. The exposed portions 54 of the photopolymer resist material 53 are then removed, leaving the finished article (shown in FIG. 2E) having protrusions 76 separated by the recesses 70.
One drawback with the method discussed above with reference to FIGS. 2A–2E is that separate steps are required to place the photopolymer resist material 53 on the substrate polymer 52 and remove the photopolymer resist material 53 from the substrate polymer 52 after the recesses 70 are formed. Furthermore, the solvent that removes the photopolymer resist material 53 may be different than the solvent that removes the underlying substrate polymer 52, requiring the manufacturer to keep multiple solvents on hand.
One method for reducing the number of manufacturing steps and solvents associated with photoresistive techniques used in the printing industry is to etch the recesses 70 directly in a photosensitive material. For example, Cyrel®, available from E.I. du Pont de Nemours and Co. of Wilmington, Del., is used to make printing plates by forming surface features directly in a photosensitive material without separately etching the material below. However, such printing plates are generally unsuitable for application to planarizing pads because the surfaces of the plates have deep recesses that separate inked regions from non-inked regions of the plates to prevent blurring of the resulting image. These deep recesses will not adequately support the planarizing liquid adjacent to the surface of a microelectronic substrate, reducing the effectiveness of the planarizing pad.